<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* 选中a标签未访问过的状态 */
    a:link {
      color: red;
    }

    /* 选中a标签访问过之后的状态 */
    a:visited {
      color: yellow;
    }

    /* 选中鼠标悬停的状态 */
    a:hover {
      color: orange;
    }

    /* 选中鼠标按下的状态 */
    a:active {
      color: skyblue;
    }
  </style>
</head>
<body>
  <a href="#">我是a标签</a>
</body>
</html>